1. Field of the Invention
The present invention relates to a weld material, in particular to a steel which contains Cr in a range from 8 to 13%, has high intensity at high temperatures, and is suitable for a gas metal arc welding, a gas metal arc welding method, and a welded structure.
This application is based on the Japanese Patent Application No. Hei 12-29582, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Recently, there is a tendency for generator boilers to be used under conditions in which the temperature and pressure are high, in order to increase their efficiency. Therefore, high Cr steels having high intensity at high temperatures, such as 9 Cr steel and 12 Cr steel, have been tested as the materials for constructing generator boilers. When high Cr steel is used for generator boilers, it is extremely important to select the best welding method for the high Cr steel.
Several high Cr steels, which can be welded by a shielded metal arc welding method, and a TIG (tungsten inert gas) welding method, have been used. For example, the Japanese Unexamined Patent Application, First publication No. Hei 02-280993 discloses a weld material containing of 0.01 to 0.1% C, 0.01 to 1% Si, 0.01 to 2.0% Mn, 8 to 12% Cr, 1 to 5% Ni, 0.1 to 3.0% Mo, 0.1 to 0.5% V,0.1 to 3% W,0.01 to 0.2% Nb, .ltoreq.0.04% Al, 0.003 to 0.08% N, .ltoreq.0.01% O, 0.0005 to 0.01% Ca, and consisting of the balance Fe with inevitable impurities, and of which the Cr equivalent (Cr eq.=Cr+6Si+4Mo+1.5 W+11V+5Nb+12Al-40C-30N-4Ni-2Mn (%)) is 13% or less and Qc (Qc=C+Mn/20+Si/30 (%)) is 0.15% or less.
Moreover, the Japanese Patent Application, First publication No. Hei 07-268563 discloses a weld material containing 0.03 to 0. 12% C, 0.01 to 0.3% Si, 0.3 to 1.5% Mn, 8 to 13% Cr, 1 to 5% Ni, 0.3 to 1.6% Mo, 0.03 to 0.40% V, 0.5 to 3.5% W, 0.01 to 0.15% Nb, 0.01 to 0.08% N, and the balance Fe with inevitable impurities, also containing at least either of 1.0 to 5.0% Co and 0.5 to 4.0% Cu, and the contents of Mo, W, Co and Cu satisfy the relationship in (Mo+W)/(Co+Cu).gtoreq.1.5 in this composition.
These high Cr steels disclosed in these prior documents were welded by the shielded metal arc welding method or the TIG welding method. However, when these high Cr steels are welded by these welding methods, the welding efficiency worsens.
A gas metal arc welding method (abbreviated as "GMA welding method" below) is well known as a welding method having a high welding efficiency, compared with the shielded metal arc welding method and the TIG welding method. The welding speed of the GMA welding method is approximately 10 times as fast as the welding speed of the shielded metal arc welding method and the TIG welding method. Therefore, in order to decrease the manufacturing cost of the generator boiler, it is desired to adopt the GMA welding method for high Cr steels.
In the GMA welding method, the circumference of an arc is shielded by inert gas such as Ar, etc. or carbon dioxide. In order to stabilize the arc, it is well known that the shielding gas necessarily contains a certain amount of oxygen. However, when a high Cr steel is welded, and the oxygen concentration in the shielding gas is high, the toughness of welded materials decreases. Therefore, the fact that the GMA welding method has been practically adopted for high Cr steels has not been reported.
In consideration of the above described problems with conventional technology, it is an object of the present invention to provide a weld material which contains 8 to 13% Cr, and can be used with the GMA welding method, a GMA welding method which has superior arc stability and can provide a welded material having superior properties, and a welded structure.